1. Field of the Invention
The present invention relates in general to a reflection type projector, and more particularly, to a reflection type projector capable of increasing the intensity of light projected onto a screen.
2. Description of the Related Art
A projector projects a formed image onto a screen using an additional light source. The projector is usually classified as a projection type projector or a reflection type projector according to the way by which the image is formed.
FIG. 1 shows an optical system of a conventional reflection type projector. The conventional reflection type projector includes a light source 10 for emitting light, a color wheel 20 for selectively transmitting a certain color of light, a scrambler 30 for mixing rays of the input light having different degrees of intensity into a uniform beam, a condensing lens 32, a collimating lens 34, a polarization beam splitter 40 for changing an optical path of the light, a display device 50 for forming an image by selectively reflecting an input light, and a projection lens unit 60 for projecting an input light onto a screen (not shown).
The light source 10 is comprised of a lamp 11, such as a metal haloid lamp or a xenon arc lamp, for generating light, and a reflection mirror 13 for reflecting the light emitted from the lamp 11. The color wheel 20 installed along the optical path of the light between the light source 10 and the scrambler 30 is rotated by a driving motor 21. The color wheel 20 is composed of color filters of red (R), green (G) and blue (B). The color wheel 20 rotates at a speed corresponding to the response speed of the display device. At any given time, one of the color filters R, G and B is disposed along the optical path of the light, according to the response speed of the display device 50.
The scrambler 30 mixes the input light through diffused reflection to make uniform light. The condensing lens 32 converges the light passing through the scrambler 30, which then diverges, to enlarge a transmission width of the light. The collimating lens 34 condenses the input divergent light to make parallel light beams.
The polarization beam splitter 40 is arranged in the optical path of the light between the collimating lens 34 and the display device 50, and changes the optical path of an input light by selectively transmitting or reflecting the input light at a mirror surface 41 according to the polarization component thereof. That is, the light input from the light source 10 is selectively transmitted or reflected depending on the polarization component of the light.
In FIG. 1, the light transmitted from the polarization beam splitter 40 is used as an efficiency light. A ferroelectric liquid crystal display (FLCD) of a two-dimensional array structure exhibiting an excellent response speed is used as the display device 50. The display device 50 has a multiplicity of reflection areas of a two-dimensional array structure, each area being independently driven to form an image by changing the polarization direction of the input light.
The light input to the display device 50 is reflected and re-enters the polarization beam splitter 40. Here, the efficiency light re-entering the polarization beam splitter 40 has had its polarization direction changed to 90xc2x0 by the display device 50. Then, the beam is reflected from the mirror surface 41 of the polarization beam splitter 40 to proceed toward the projection lens unit 60. The beam passes through the projection lens unit 60 and is projected onto a screen (not shown).
As described above, the conventional reflection type projector requires parallel beams of light to be input into the polarization beam splitter, to avoid deterioration of the transmission/reflection according to the polarization component. Thus, the width of the light input into the polarization beams splitter must be increased to make the parallel beam between the light source and the polarization beam splitter, which also requires a larger polarization beam splitter and projection lens unit, which are expensive.
In another reflection type projector employing an FLCD, instead of the polarization beam splitter, the angle of the light input into the FLCD is different from that reflected therefrom, to thereby change the path of the light. Here, the FLCD is smaller than the collimating lens. Therefore, the optical distance between the FLCD and the projection lens unit must be lengthened or the slope of the FLCD must be increased. When the optical distance is lengthened, the diameter of the projection lens unit is reduced. On the other hand, an increase in the slope of the FLCD complicates the arrangement of optical axes between the FLCD and the projection lens unit.
To solve the above problems, it is an objective of the present invention to provide a reflection type projector having a critical angle prism which changes the path of light, to thereby simplify the arrangement of optical axes without the use of a polarization beam splitter or the increase in optical length.
It is another objective of the present invention to provide a reflection type projector in which three colors are irradiated onto a screen to improve optical efficiency and increase the intensity of the light projected on the screen.
Accordingly, to achieve the above first objective, there is provided a reflection type projector including: a light source for generating and emitting light; an image generation unit having a multiplicity of pixels in a two-dimensional array structure, each of the pixels being independently driven, for forming and reflecting an image from the input light; a critical angle prism having a transmission/reflection surface disposed along an optical path of the light, to transmit the light input from the light source and reflect the light re-entering from the image forming unit; and a projection lens unit for enlarging and transmitting the light reflected from the transmission/reflection surface of the critical angle prism onto a screen.
To achieve the second objective, there is provided a reflection type projector including: a light source for generating and emitting light; a first dichroic mirror, disposed along an optical path, for transmitting and reflecting input light according to a wavelength to divide the transmitted and reflected light into two; a first optical path changing unit for changing the path of one light beam divided by the first dichroic mirror; a first image forming unit for generating an image from input light passing through the first optical path changing unit; a second dichroic mirror for transmitting and reflecting the light reflected from the first dichroic mirror according to wavelength; a second optical path changing unit for changing the path of the other light beam divided by the second dichroic mirror; a second image forming unit for generating an image from input light passing through the second optical path changing unit; a third optical path changing unit for changing the path of the light transmitting the second dichroic mirror: a third image forming unit for generating an image from input light passing through the third optical path changing unit; a dichroic beam splitter having first and second mirror surfaces for selectively transmitting and reflecting the input light passing through the first, second and third optical path changing units in one direction according to wavelength; and a projection lens unit for enlarging and transmitting the light input from the dichroic beam splitter onto a screen.
The above and other features of the invention including various and novel details of construction and combination of parts will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular reflection type projector embodying the invention is shown by way of illustration only and not as a limitation of the invention. The principles and features of this invention may be employed in varied and numerous embodiments without departing from the scope of the invention.